ASTM D5621 Standard Test Method for Sonic Shear Stability of Hydraulic Fluids
7. Calibration of Apparatus
7.1 The reference fluid provides a practical way to define the performance (severity level) of a sonic oscillator unit so that satisfactory comparison can be made between tests run on different days in the same unit and between tests run with different units.
7.2 The decrease in viscosity observed for a given hydraulic fluid on irradiation in an oscillator unit depends on a number of factors; these include sample volume, irradiation time, and oscillator power setting. Frequency of the generator is 23 +/- 2 kHz. Typical power settings are in the range of 50 watts. Manual tuning of the oscillator-horn combination is also required in some instruments in order to ensure efficiency of energy coupling between the two units. The procedure described in 7.3 is recommended for establishing a reproducible performance level for a given unit.
7.3 Confirm and record the 40°C viscosity of the reference fluid. Introduce 30 mL (room temperature) of the reference fluid into the 50-mL Griffin beaker. Immerse the beaker in ice water or a constant temperature bath at 0°C until the sample fluid level is below the liquid level in the bath. The beaker should be maintained in a vertical position in the bath. Secure beaker in this position and condition the sample for 12.5 min before commencing irradiation. Immerse the sonic horn into the sample fluid until the tip is at least 10 mm below the surface of fluid (see Fig. 1) in order to ensure that the tip remains submerged during the test. Exercise care to avoid contact of the tip with the bottom of the beaker as this will shorten tip life. The horn should be placed in a vertical position in the fluid and centered in the beaker (a weighted ring stand may be used to support the horn in this position). True vertical positioning is not critical and is intended primarily to minimize liquid splashing during irradiation. Irradiate the fluid for 12.5 min at a preselected power setting. Determine the decrease in reference fluid viscosity measured at 40°C. Repeat as necessary to determine the proper power setting to produce a viscosity change at 40°C of 15.0 % (+/- 1 %). Use this power setting for subsequent test runs. Daily recalibration of the apparatus is required because the power setting required to produce a stated viscosity loss will probably vary from day to day. Experience with a given apparatus set will determine whether more frequent calibration is required. Calibration in this manner will ensure that repeatable severity levels are established.
